The present invention relates to Eimeria polypeptides, DNA-fragments encoding those peptides, recombinant DNA molecules comprising such fragments, live recombinant carriers comprising such fragments or molecules, host cells comprising such fragments, molecules or carriers, antibodies against the polypeptide and coccidiosis vaccines. The invention also relates to methods for the preparation of such antibodies and vaccines, and to methods for the detection of Eimeria parasites and antibodies against Eimeria parasites.
Parasitic protozoa belonging to the genus Eimeria are the causative agents of intestinal coccidiosis, an enteritis which affects birds. This causes significant economic loss, especially to the poultry industry. (For the purposes of the present application, the term xe2x80x9cpoultryxe2x80x9d is taken to mean birds that serve as sources of eggs or meat. It includes, inter alia, chickens, turkeys, ducks, geese, guinea fowl, pheasants, pigeons and pea fowl). Nowadays, coccidiosis is mainly controlled by the use of antibiotic drugs in the feed. The rapid emergence of drug resistant strains (Chapman H. D. Parasitology Today 9, 159-162 (1993)) and the prohibitive costs of development and registration of a novel drug have led to increased interest in the development of an alternative method of control. The development of effective vaccines has therefore been desirable for many years. However only partial success has been obtained.
Currently available vaccination strategies consist of Controlled infections with either virulent or live attenuated parasites (Shirley M. W. In: Proceedings of the VIth. International Coccidiosis Conference (Eds.: J. R. Barta and M. A. Fernando) Moffitt Print Craft Ltd., Guelph. pp. 61-72 (1993)). For reasons of safety and cost, the most desirable method of immunoprophylaxis against coccidiosis appears to be the use of a subunit vaccine. Although many attempts have been made to immunise chickens against coccidiosis with fractions of parasite material (Murray P. K., Bhogal B. S., Crane M. S. J. and MacDonald T. T. In: Research in Avian Coccidiosis. Proceedings of the Georgia Coccidiosis Conference (Eds.: L. R. McDougald, Joyner L. P. and P. L. Long) Athens, University of Georgia. pp. 564-573 (1986), McKenzie M. E. and Long P. L. Poultry Science 65, 892-897 (1986)) or recombinant Eimeria polypeptides (Danforth H. D., Augustine P. C., Ruff M. D., McCandliss R., Strausberg R. L. and Likel M. Poultry Science 68, 1643-1652 (1989), Jenkins M. C., Augustine P. C., Danforth H. D. and Barta J. R. Infection and Immunity 59, 4042-4048 (1991)) only limited protection against challenge infection could be achieved. The parasite stages responsible for the induction of protective immunity are generally thought to be early asexual developmental stages (Jenkins et al. 1991). Initially, selection of candidate antigens was performed using antibodies from immune chickens but, in view of the fundamental role of cell mediated responses in protective immunity (reviewed in Lillehoj H. S. and Trout J. M. Avian Pathology 22, 3-31 (1993), Rose M. E. In: Poultry Immunology (Ed.: T. F. Davison, T. R. Morris and L. N. Payne), Carfax Publishing Company, Oxfordshire, U.K. pp. 265-299 (1996), attention has now focused, next to B-cell inducing antigens, on screening antigens for their ability to stimulate specific T-cell responses (Dunn P. P. J., Billington K., Bumstead J. M. and Tomley F. M. Molecular and Biochemical Parasitology 70, 211-215 (1995)).
It is an objective of the present invention to provide polypeptides that are capable of inducing protection against the pathogenic effects of Eimeria infection in poultry.
It was now surprisingly found that 6 different polypeptides could be specifically identified and isolated, essentially free from other Eimeria polypeptides, from a hydrophilic fraction of Eimeria polypeptides, each of these different polypeptides being capable of inducing an immune response against Eimeria parasites. The inventors have found that these polypeptides can be used, either alone or in combination with each other, to provide a vaccine which gives a significant degree of protection to birds (preferably poultry). For example, protection against the formation of cecal lesions can be achieved in birds immunised with such a vaccine, when subjected to subsequent challenge with Eimeria parasites.
A first embodiment of the invention relates to a hydrophilic polypeptide of Eimeria that in its full-length form has a molecular weight of 25 kD and comprises an amino acid sequence that shares at least 70% homology with the amino acid sequence MPFELPPLPYPMDALEPYISKETLEYHYGKHHAAYVNNLNRLVEGKPEASKSLEEIIKT SSGSVLNNAGQAWNHTFYWKSMRPASAGGPPGAPGGGPPGAPGAPLREELESAFG GVEKFREAFAAAAAAHFGSGWAWLCFCKKSRSLFLLQTHDGATPFRDNPNCAPLLTC DLWEHAYYIDRRNDRKSYLDAWWSVVNWDFANENLKKAMQGSD (further referred to as SEQ ID NO: 1:) and immunogenic fragments of that polypeptide capable of inducing an immune response against said polypeptide. The polypeptide is functionally related to a Superoxide Dismutase (SOD) found in non-Eimeria parasites and is therefore characterised as SOD-like.
Also, this embodiment relates to a hydrophilic polypeptide of Eimeria that is a peroxidoxin-like polypeptide, in its full-length form has a molecular weight of 22 kD and comprises an amino acid sequence that shares at least 70% homology with the amino acid sequence LGPLALPLLADVR (further referred to as SEQ ID NO: 2:), and immunogenic fragments of the polypeptide capable of inducing an immune response against that polypeptide.
A hydrophilic polypeptide of Eimeria that is a peroxidoxin-like polypeptide, in its full-length form has a molecular weight of 25 kD and comprises an amino acid sequence that shares at least 70% homology with the amino acid sequence MPLNLGDSFPDFQAEALGAEHFRLHEYLGDSWGVMFSHPNDFTPVCTTELAEAVKLQ DSFTKKNCKLVGFSCNDLQSHREWAKDIMAYAGRSGNLPFPLVCDPNRELAASLGIM DPAEKDKKGLPLTCRCVFFISPEKKLAASILYPATTGRNFAEILRVLDSLQLTAKFPVAT PVDWTAGAKCCVVPNLAAEEAQRLLPKGHEALQLPSGKPYLRLTPDPRG (further referred to as SEQ ID NO: 3:), as well as immunogenic fragments of the polypeptide capable of inducing an immune response against that polypeptide are also part of this embodiment.
Also part of this embodiment is a hydrophilic polypeptide of Eimeria that in its full-length form has a molecular weight of 22 kD and comprises an amino acid sequence that shares at least 70% homology with the amino acid sequence MSPSPAGVAEYLASL (further referred to as SEQ ID NO: 4:), or an immunogenic fragment of that polypeptide capable of inducing an immune response against said polypeptide.
This embodiment also includes a triosephosphate isomerase-like hydrophilic polypeptide of Eimeria that in its full-length form has a molecular weight of 28 kD and comprises an amino acid sequence that shares at least 70% homology with the amino acid sequence NHAEFDPSQTEVVVFP (further referred to as SEQ ID NO: 5:), or an immunogenic fragment of that polypeptide capable of inducing an immune response against said polypeptide.
Finally, this embodiment relates to a hydrophilic polypeptide of Eimeria that in its full-length form has a molecular weight of 28 kD and comprises an amino acid sequence that shares at least 70% homology with the amino acid sequence VDSFTPSVGCVFAGMPADFR (further referred to as SEQ ID NO: 6:), or an immunogenic fragment of that polypeptide capable of inducing an immune response against said polypeptide.
Although various groups have disclosed Eimeria derived proteins which might, by chance, have molecular masses within the 26-30 kDaxc2x15 kDa range disclosed above, these proteins are quite different from the polypeptides of the present invention.
For example, in EP-A-0231537 (Newman et al) a 25 kDa surface protein is disclosed. However under reducing conditions this splits to form two bands on SDS-PAGE of about 17 and about 8 kDa, whereas the polypeptides of the present invention had relative molecular masses of at least 21 kDa when separated under reducing conditions.
Bouvier et al (J. Biol. Chem. (1985) 260(29); pp15504-15509) teach that using Triton X114 extraction amphiphilic proteins (membrane-associated) are only detected in the detergent phase and not in the hydrophilic phase.
In U.S. Pat. No. 4,710,377 (Schenkel et al) antigens are disclosed with molecular masses of about 28 and 26 kDa. However these are amphiphilic outer-membrane components and would not therefore be present in the hydrophilic phase of a Triton X-114 extract which could be used to prepare polypeptides of the present invention.
Eimeria proteins that are amphiphilic are also disclosed in WO92/04461 (Jacobson et al), EP-A-0324648 (Liberator et al), AU-A-28542/49 (Turner et al), EP-A-0344808 (Alternburger et al) and EP-A-0167443 (Murray et al).
It will be understood that, for the particular hydrophilic polypeptides embraced herein, natural variations can exist between individual Eimeria parasites or strains. These variations may exist in (an) amino acid difference(s) in the overall sequence or by deletions, substitutions, insertions, inversions or additions of (an) amino acid(s) in said sequence. Amino acid substitutions which do not essentially alter biological and immunological activities, have been described, e.g. by Neurath et al in xe2x80x9cThe Proteinsxe2x80x9d Academic Press New York (1979). Amino acid replacements between related amino acids or replacements which have occurred frequently in evolution are, inter alia, Ser/Ala, Ser/Gly, Asp/Gly, Asp/Asn, Ile/Val (see Dayhof, M. D., Atlas of protein sequence and structure, Nat. Biomed. Res. Found., Washington D.C., 1978, vol. 5, suppl. 3). Other amino acid substitutions include Asp/Glu, Thr/Ser, Ala/Gly, Ala/Thr, Ser/Asn, Ala/Val, Thr/Phe, Ala/Pro, Lys/Arg, Leu/Ile, Leu/Val and Ala/Glu. Based on this information, Lipman and Pearson developed a method for rapid and sensitive protein comparison (Science, 227, 1435-1441, 1985) and determining the functional similarity between homologous proteins. Such amino acid substitutions of the exemplary embodiments of this invention are within the scope of the invention as long as the resulting polypeptides retain their immunoreactivity. Thus, natural variations not essentially influencing the immunogenicity of the polypeptide compared to the wild-type polypeptide, are considered immunologically equivalent variants of the polypeptides according to the invention.
Therefore, a polypeptide having a variant amino acid sequence, that has at least 70% homology to respectively the amino acid sequence MPFELPPLPYPMDALEPYISKETLEYHYGKHHAAYVNNLNRLVEGKPEASKSLEEIIKT SSGSVLNNAGQAWNHTFYWKSMRPASAGGPPGAPGGGPPGAPGAPLREELESAFG GVEKFREAFAAAAAAHFGSGWAWLCFCKKSRSLFLLQTHDGATPFRDNPNCAPLLTC DLWEHAYYIDRRNDRKSYLDAWWSVVNWDFANENLKKAMQGSD, LGPLALPLLADVR, MPLNLGDSFPDFQAEALGAEHFRLHEYLGDSWGVMFSHPNDFTPVCTTELAEAVKLQ DSFTKKNCKLVGFSCNDLQSHREWAKDIMAYAGRSGNLPFPLVCDPNRELAASLGIM DPAEKDKKGLPLTCRCVFFISPEKKLAASILYPATTGRNFAEILRVLDSLQLTAKFPVAT PVDWTAGAKCCVVPNLAAEEAQRLLPKGHEALQLPSGKPYLRLTPDPRG, MSPSPAGVAEYLASL, NHAEFDPSQTEVVVFP and VDSFTPSVGCVFAGMPADFR as depicted in SEQ ID NO: 1-6 is also considered to fall within the scope of the invention.
The level of homology is defined by the following formula: H=m/nxc3x97100%, wherein H is the percentage homology, m is the number of identical amino acids in the sequence and n is the total number of amino acids. The amino acid sequence ABCDEEGHIJK, when compared to ABCDEFGHIJK, would then be 10/11xc3x97100%=90.9% homologous. The amino acid sequence ABCDEGHIJK would also be 10/11xc3x97100%=90.9% homologous: there would just be a gap at the spot where one sequence has the F and the other sequence has not.
When a polypeptide is used for e.g. vaccination purposes or for raising antibodies, it is however not necessary to use the whole polypeptide. It is also possible to use a fragment of that polypeptide that is capable of inducing an immune response against that polypeptide, a so-called immunogenic fragment.
An xe2x80x9cimmunogenic fragmentxe2x80x9d is understood to be a fragment of the full-length protein, that still has retained its capability to induce an immune response in the host. At this moment, a variety of techniques is available to easily identify antigenic fragments (determinants). The method described by Geysen et al (Patent Application WO 84/03564, Patent Application WO 86/06487, U.S. Pat. No. 4,833,092, Proc. Natl Acad. Sci. 81: 3998-4002 (1984), J. Imm. Meth. 102, 259-274 (1987), the so-called PEPSCAN method is an easy to perform, quick and well-established method for the detection of epitopes; the immunologically important regions of the protein, used world-wide and as such well-known to man skilled in the art. This (empirical) method is especially suitable for the detection of B-cell epitopes. Also, given the sequence of the gene encoding any protein, computer algorithms are able to designate specific polypeptide fragments as the immunologically important epitopes on the basis of their sequential and/or structural homology with epitopes that are now known. The determination of these regions is based on a combination of the hydrophilicity criteria according to Hopp and Woods (Proc. Natl. Acad. Sci. 78: 38248-3828 (1981)), and the secondary structure aspects according to Chou and Fasman (Advances in Enzymology 47: 45-148 (1987) and U.S. Pat. No. 4,554,101).
T-cell epitopes can likewise be predicted from the sequence by computer with the aid of Berzofsky""s amphiphilicity criterion (Science 235, 1059-1062 (1987) and US Patent application NTIS U.S. Ser. No. 07/005,885). A condensed overview is found in: Shan Lu on common principles: Tibtech 9: 238-242 (1991), Good et al on Malaria epitopes; Science 235: 1059-1062 (1987), Lu for a review; Vaccine 10: 3-7 (1992), Berzofsky for HIV-epitopes; The FASEB Journal 5:2412-2418 (1991)
Therefore, this embodiment of the invention not only relates to polypeptides according to the invention, but also to fragments of those polypeptides that are still capable of inducing an immune response against the polypeptides (so-called immunogenic fragments).
In a preferred form of this embodiment, a hydrophilic polypeptide is provided, that comprises an amino acid sequence that is at least 80% homologous to the sequence given in one of the SEQ ID NO: 1-6.
In a more preferred form of this embodiment, the amino acid sequence is at least 90% homologous to the sequence given in one of the SEQ ID NO: 1-6.
In an even more preferred form of this embodiment, the amino acid sequence is the sequence given in one of the SEQ ID NO: 1-6.
Preferably the polypeptide according to the invention is isolated from Eimeria tenella. 
Another embodiment of the invention relates to DNA fragments encoding a polypeptide of the present invention or immunogenic fragments thereof. Since for the first time the partial amino acid sequence of the polypeptides according to the invention is now provided, man skilled in the art can (using the genetic code table found in biochemistry textbooks as e.g. in Lubert Stryer""s Biochemistry, Ed. Freeman and Company, New York) easily prepare a mixed DNA probe and select the gene encoding the polypeptide according to the invention from Eimeria.
There may be minor variations in the overall nucleotide sequence of the DNA encoding the polypeptides according to the invention in the respective Eimeria strains. These variations may have no effect on the amino acid sequence of the polypeptide, in case that the modification is such that the variant triplet codes for the same amino acid. This cause of variation is based upon the phenomenon of degeneracy of the genetic code. It happens e.g. that due to natural mutation the G in the triplet CTG, coding for the amino acid Leucine, is replaced by a C, also coding for Leucine, or that the A in GAA coding for glutamic acid is replaced by a G, which triplet still encodes glutamic acid. Such a mutation is a silent mutation, i.e. it does not show at the amino acid level. Such silent modifications are very frequently found in nature, when comparing e.g. two different field isolates of Eimeria. This phenomenon is found for all amino acids, except Met and Trp. Thus, it is obvious, that the polypeptides of the present invention can be encoded by a very large variety of other sequences, all encoding the identical polypeptide. It therefore goes without saying that any nucleic acid sequence encoding a polypeptide comprising an amino acid sequence that is at least 70% homologous to the amino acid sequence as depicted in SEQ ID NO: 1-6 of the present invention or an immunogenic fragment thereof is also considered to fall within the scope of the invention.
Merely for the purpose of giving an example, all possible probes for detecting the gene encoding the 25 kD SOD-like hydrophilic Eimeria polypeptide comprising i.a. the amino acid sequence YLDAWWSVVNWDFANENLK (part of SEQ ID NO: 1:) are given in SEQ ID NO: 7-38. In these SEQ IDs, all possible nucleic acid sequences are listed that code for the amino acid sequence VNWDFA of SEQ ID NO: 1:. Of the 32 probes, one has by definition a perfect fit with each DNA fragment comprising a nucleic acid sequence encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 1.
As described i.a. in Maniatis/Sambrook (Sambrook, J. et al. Molecular cloning: a laboratory manual. ISBN 0-87969-309-6) hybridisation of probes to DNA is done at 12xc2x0 C. below Tm, where Tm=69.3+0.41xc3x97(G+C)%xe2x88x92650/L (L=length of the probe). That means that under stringent conditions (a hybridisation temperature of between 38 and 48 degrees Celsius), the gene encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 1 can always be picked up selectively and free from false hybridisation signals, using the probes of SEQ ID NO: 7-38. Such mixed probes very easily made using standard procedures in e.g. one of the many commercially available automatic DNA synthesizers.
For the reasons given above, especially a mixed DNA probe encoding the whole amino acid sequence of one of the amino acid sequences given in SEQ ID NO: 1-6 can be used to detect the genes encoding the polypeptides according to the invention in Eimeria.
Identification and cloning of the genes encoding the polypeptides according to the invention in Eimeria, not only for tenella but also for the other species, can easily be done as follows: first strand cDNA can be hybridised with both a mixed probe for one of the polypeptides according to the invention and an oligo-dT probe. The DNA fragment between both probes can then be multiplied in a standard PCR reaction. (PCR-techniques are e.g. described in Maniatis/Sambrook (Sambrook, J. Molecular cloning: a laboratory manual. ISBN 0-87969-309-6)). The PCR fragment can then be cloned into a plasmid and e.g. be used for sequencing or for detection of the full length gene in the genome of any Eimeria species.
This method allows an easy and straightforward selection and sequencing of the genes encoding the polypeptides according to the invention, not only from Eimeria tenella but also from other Eimeria species such as necatrix, brunette, mitis or acervulina. 
Thus, in another embodiment, the invention relates to a DNA fragment comprising a nucleotide sequence encoding a polypeptide according to the invention or an immunogenic fragment thereof.
The mixed probe method described above for the detection of the DNAs encoding the various polypeptides according to the invention has e.g. been used to obtain the DNA encoding the 25 kD SOD-like polypeptide according to the invention in Eimeria tenella. Using the method described in the Examples, a DNA fragment encoding practically the whole 25 kD SOD-like polypeptide of Eimeria tenella could be isolated, cloned and sequenced. The sequence of that DNA-fragment was found to be ATGCCGTTCGAACTCCCCCCGCTGCCGTACCCCATGGACGCCCTCGAGCCGTAC ATCAGCAAAGAGACTCTCGAGTACCACTATGGGAAGCACCACGCGGCTTACGTGA ACAACTTGAACAGACTCGTCGAGGGGAAGCCGGAGGCTTCCAAGAGCCTGGAGG AAATAATAAAGACCTCCTCGGGGTCGGTGCTGAACAACGCGGGCCAGGCGTGGA ACCACACGTTCTACTGGAAGTCGATGCGGCCGGCCTCGGCGGGGGGCCCCCCG GGGGCCCCCGGCGGGGGCCCCCCGGGGGCCCCGGGGGCCCCCCTGCGGGAG GAGCTGGAGAGCGCGTTCGGGGGCGTGGAGAAGTTCCGGGAGGCCTTTGCTGCT GCTGCTGCTGCGCACTTCGGCTCGGGCTGGGCCTGGCTCTGCTTCTGCAAGAAG TCCCGCAGCCTCTTTTTGCTGCAGACCCACGACGGGGCCACGCCTTTCAGAGACA ACCCCAACTGCGCGCCGCTGCTCACCTGCGACCTGTGGGAGCACGCCTACTACA TCGACCGCAGAAACGACCGCAAGAGCTACCTCGACGCGTGGTGGTCTGTGGTGA ATTGGGACTTCGCGAACGAGAACTTGAAGAAGGCAATGCAGGGAAGCGACTAGG CGCGTGGTGGTCTGTGGTGAATTGGGACTTCGCGAACGAGAACTTGAAGAAGGC AATGCAGGGAAGCGACTAG and will be further referred to as SEQ ID NO: 39:
Therefore a preferred form of this embodiment relates to a DNA fragment comprising a nucleotide sequence as depicted in SEQ ID NO: 39:
The mixed probe method was also used to obtain the DNA encoding the 25 kD peroxidoxin-like polypeptide according to the invention in Eimeria tenella. Using the method described in the Examples, a DNA fragment encoding a large part of the whole 25 kD peroxidoxin-like polypeptide of Eimeria tenella could be isolated, cloned and sequenced. In addition, the genomic sequence, i.e. the sequence of the part of the gene as found in the Eimeria tenella genome was found to be TTCCCGGATTTTCAGGCGGAGGCGCTGGGCGCCGAGCACTTCCGCTTGCACGAG TACTTGGGGGACAGCTGGGGAGTGATGTTCAGgtaagattggcgtaaaaaagccccatttaatcg cattttaattctgtagactctgtgtcgactgctgagcacgaggggggggcctgctgcacgggagagccttgtctcgcgctc aactctgggtttctggcgttgcttgcagCCACCCGAACGACTTCACCCCCGTCTGCACCACCGA.
This sequence is further referred to as SEQ ID NO: 40:
Upper case letters indicate the sequence also found in the mRNA, small letters indicate the intron in the gene.
Therefore another preferred form of this embodiment relates to a DNA fragment comprising a nucleotide sequence as depicted in SEQ ID NO: 40:
The cDNA encoding the mRNA for this polypeptide was also detected using the mixed probe approach. This cDNA was sequenced and found to have the following sequence:
ATGCCGTTGAACTTGGGAGATTCCTTTCCAGACTTCCAGGCGGAGGCGCTGGGC GCCGAGCACTTCCGCTTGCACGAGTACTTGGGGGACAGCTGGGGAGTGATGTTC AGCCACCCGAACGACTTCACTCCCGTTTGCACAACGGAGCTCGCCGAAGCCGTG AAGCTCCAGGACTCCTTCACGAAGAAGAACTGCAAACTCGTTGGCTTCTCCTGCA ACGACCTGCAGAGCCACAGAGAATGGGCGAAGGATATAATGGCCTATGCAGGCC GATCTGGGAACTTGCCGTTTCCCCTCGTTTGCGACCCCAATAGGGAACTGGCCGC GAGTTTGGGAATTATGGATCCTGCAGAAAAGGACAAAAAGGGGCTGCCTTTGACT TGCCGCTGCGTCTTTTTCATAAGTCCAGAGAAGAAGCTCGCGGCCTCTATTTTGTA CCCGGCTACCACCGGGAGAAACTTCGCGGAAATCCTTAGGGTCCTGGACTCTCTG CAGCTCACTGCCAAGTTTCCAGTGGCCACTCCAGTGGACTGGACCGCTGGGGCC AAATGCTGCGTAGTGCCGAACTTGGCAGCAGAAGAGGCCCAAAGGCTTTTGCCCA AAGGCCACGAGGCGCTGCAGCTGCCTTCGGGGAAGCCTTACCTGCGGCTCACCC CAGACCCCAGGGGCTGA. This sequence is further referred to as SEQ ID NO: 41:
Thus, still another preferred form of this embodiment relates to a DNA fragment comprising a nucleotide sequence as depicted in SEQ ID NO: 41:
The polypeptides of the present invention can be isolated from Eimeria parasites using any standard isolation procedure known in the art for isolating Eimeria polypeptides. The polypeptides are e.g. obtainable as described in the Examples. They can be used subsequently for e.g. the preparation of a vaccine or for raising antibodies.
Alternatively a DNA fragment according to the invention can be expressed in an in vitro expression system and the expression product, the polypeptide according to the invention, can be used e.g. for vaccine or antibody preparations.
An essential requirement for the expression of the DNA fragment is an adequate promoter operably linked to the fragment. It is obvious to those skilled in the art that the choice of a promoter extends to any eukaryotic, prokaryotic or viral promoter capable of directing gene transcription in cells used as host cells for protein expression.
Therefore, a preferred form of this embodiment relates to recombinant DNA fragments, i.e. DNA fragments according to the invention, to which regulating sequences enabling expression of that nucleic acid sequence have been added by means of e.g. standard molecular biology techniques. (Maniatis/Sambrook (Sambrook, J. Molecular cloning: a laboratory manual. ISBN 0-87969-309-6))
When the host cells are bacteria, useful expression control sequences which may be used include the Trp promoter and operator (Goeddel, et al., Nucl. Acids Res., 8, 4057, 1980); the lac promoter and operator (Chang, et al., Nature, 275, 615, 1978); the outer membrane protein promoter (Nakamura, K. and Inouge, M., EMBO J., 1, 771-775, 1982); the bacteriophage lambda promoters and operators (Remaut, E. et al., Nucl. Acids Res., 11, 4677-4688, 1983); the xcex1-amylase (B. subtilis) promoter and operator, termination sequences and other expression enhancement and control sequences compatible with the selected host cell.
When the host cell is yeast, useful expression control sequences include, e.g., (xcex1-mating factor. For insect cells the polyhedrin or p10 promoters of baculoviruses can be used (Smith, G. E. et al., Mol. Cell. Biol. 3, 2156-65, 1983). When the host cell is of mammalian origin illustrative useful expression control sequences include the SV40 promoter (Berman, P. W. et al., Science, 222, 524-527, 1983) or the metallothionein promoter (Brinster, R. L., Nature, 296, 3942, 1982) or a heat shock promoter (Voellmy et al., Proc. Natl. Acad. Sci. USA. 82, 4949-53, 1985). Alternatively, expression control sequences present in Eimeria may also be applied. For maximising gene expression, see also Roberts and Lauer (Methods in Enzymology, 68, 473, 1979).
Bacterial, yeast, fungal, insect and mammalian cell expression systems are very frequently used systems. Such systems are well-known in the art and easily available, e.g. commercially through Clontech Laboratories, Inc. 4030 Fabian Way, Palo Alto, Calif. 94303-4607, USA. Next to these expression systems, parasite-based expression systems are very attractive expression systems. Such systems are e.g. described in the French Patent Application with Publication number 2 714 074, and in US-NTIS publication No U.S. Ser. No. 08/043109 (Hoffman, S and Rogers, W.: public. Date, Dec. 1, 1993).
Therefore, in a more preferred form of this embodiment the invention relates to a recombinant DNA molecule encoding the polypeptide fragment under the control of regulating sequences enabling expression of the protein encoded by said nucleic acid sequence.
Another embodiment of the invention relates to Live Recombinant Carriers (LRCs) comprising a DNA fragment or a recombinant DNA molecule according to the invention encoding a polypeptide according to the invention or an immunogenic fragment thereof. Such Live Recombinant Carriers are e.g. bacteria, parasites and viruses. These LRC micro-organisms are micro-organisms in which additional genetic information has been cloned. Animals infected with such LRCs will produce an immunogenic response not only against the immunogens of the LRC, but also against the immunogenic parts of the polypeptide(s) for which the genetic code is additionally cloned into the LRC, e.g. the polypeptide according to the invention.
As an example of bacterial LRCs, attenuated Salmonella strains known in the art can attractively be used. Also, LRC viruses may be used as a way of transporting the DNA fragment into a target cell.
Live recombinant carrier parasites have i.a. been described by Vermeulen, A. N. (Int. Journ. Parasitol. 28: 1121-1130 (1998))
Live recombinant carrier viruses are also called vector viruses. The site of integration of the DNA encoding the polypeptide according to the invention or an immunogenic fragment thereof may be a site in a viral gene that is not essential to the virus, or a site in an intergenic region. Viruses often used as vectors are Vaccinia viruses (Panicali et al; Proc. Natl. Acad. Sci. USA, 79: 4927 (1982), Herpesviruses (E.P.A. 0473210A2), and Retroviruses (Valerio, D. et al; in Baum, S. J., Dicke, K. A., Lotzova, E. and Pluznik, D. H. (Eds.), Experimental Haematology todayxe2x80x941988. Springer Verlag, New York: pp. 92-99 (1989)).
Especially fowlpox virus, a vaccinia virus infectious to poultry, and Herpesvirus of Turkeys (HVT) are very attractive live recombinant carrier viruses for carrying DNA encoding a polypeptide of the invention or an immunogenic fragment thereof.
The invention also relates to a host cell containing a DNA fragment according to the invention, to a host cell containing a recombinant DNA molecule containing a DNA fragment according to the invention under the control of regulating sequences enabling expression of the protein encoded by said nucleic acid sequence and to a host cell containing a Live Recombinamt Carrier micro-organism (LCR) containing a DNA fragment according to the invention.
A host cell may be a cell of bacterial origin, e.g. Escherichia coli, Bacillus subtilus and Lactobacillus species, in combination with bacteria-based vectors as pBR322, or bacterial expression vectors as pGEX, or with bacteriophages. The host cell may also be of eukaryotic origin, e.g. yeast-cells in combination with yeast-specific vector molecules, or higher eukaryotic cells like insect cells (Luckow et al; Bio-technology 6: 47-55 (1988)) in combination with vectors or recombinant baculoviruses, plant cells in combination with e.g. Ti-plasmid based vectors or plant viral vectors (Barton, K. A. et al; Cell 32: 1033 (1983), mammalian cells like Hela cells, Chinese Hamster Ovary cells (CHO) or Crandell Feline Kidney-cells, also with appropriate vectors or recombinant viruses.
The technique of in vivo homologous recombination, well-known in the art, can be used to introduce a recombinant nucleic acid sequence into the genome of a bacterium, parasite or virus of choice, capable of inducing expression of the inserted gene in the host animal.
Another embodiment of the invention relates to vaccines capable of protecting poultry against the pathogenic effects of Eimeria infection. Vaccines according to the present invention can be made e.g. by merely admixing of a polypeptide according to the invention or an immunogenic fragment thereof and a pharmaceutically acceptable carrier. A pharmaceutically acceptable carrier is understood to be a compound that does not adversely effect the health of the animal to be vaccinated, at least not to the extend that the adverse effect is worse than the effects seen due to illness when the animal is not vaccinated. A pharmaceutically acceptable carrier can be e.g. sterile water or a sterile physiological salt solution. In a more complex form, the carrier can e.g. be a buffer.
The vaccine according to the present invention may in a preferred presentation also contain an adjuvant. Adjuvants in general comprise substances that boost the immune response of the host in a non-specific manner. A number of different adjuvants are known in the art. Examples of adjuvants are Freunds Complete and Incomplete adjuvant, vitamin E, non-ionic block polymers and polyamines such as dextransulphate, carbopol and pyran. Also very suitable are surface active substances such as Span, Tween, hexadecylamine, lysolecitin, methoxyhexadecylglycerol and saponins such as Quill A(copyright). A preferred adjuvant is Quill A. This may be administered at a level of around 150 xcexcg/dose (for example). Furthermore, peptides such as muramyldipeptides, dimethylglycine, tuftsin, are often used. Next to these adjuvants, Immune-stimulating Complexes (ISCOMS), mineral oil e.g. Bayol(copyright) or Markol(copyright), vegetable oils or emulsions thereof and Diluvac(copyright) Forte can advantageously be used. The vaccine may also comprise a so-called xe2x80x9cvehiclexe2x80x9d. A vehicle is a compound to which the polypeptide adheres, without being covalently bound to it. Often used vehicle compounds are e.g. aluminium hydroxide, -phosphate, sulphate or -oxide, silica, Kaolin, and Bentonite. A special form of such a vehicle, in which the antigen is partially embedded in the vehicle, is the so-called ISCOM (EP 109.942, EP 180.564, EP 242.380). A preferred adjuvant is Quill A. This may be administered at a level of around 150 xcexcg/dose (for example).
Often, the vaccine is mixed with stabilisers, e.g. to protect degradation-prone polypeptides from being degraded, to enhance the shelf-life of the vaccine, or to improve freeze-drying efficiency. Useful stabilisers are i.a. SPGA (Bovarnik et al; J. Bacteriology 59: 509 (1950)), skimmed milk, gelatin, bovine serum albumin, carbohydrates e.g. sorbitol, mannitol, trehalose, starch, sucrose, dextran or glucose, proteins such as albumin or casein or degradation products thereof, and buffers, such as alkali metal phosphates.
Freeze-drying is an efficient method for conservation. Freeze-dried material can be stored and kept viable for many years. Storage temperatures for freeze-dried material may well be above zero degrees, without being detrimental to the material.
Freeze-drying can be done according to all well-known standard freeze-drying procedures.
Therefore, in a most preferred embodiment, the vaccine is in a freeze-dried form.
In addition, the vaccine may be suspended in a physiologically acceptable diluent. Such a diluent can e.g. be as simple as sterile water, or a physiological salt solution.
It goes without saying, that other ways of adjuvating, adding vehicle compounds or diluents, emulsifying or stabilising a polypeptide are also embodied in the present invention.
The vaccine according to the invention can be administered in a conventional active immunisation scheme: single or repeated administration in a manner compatible with the dosage formulation, and in such amount as will be prophylactically effective, i.e. the amount of immunising antigen or recombinant micro-organism capable of expressing said antigen that will induce immunity in birds (especially poultry) against challenge by virulent Eimeria parasites. Immunity is defined as the induction of a significant level of protection in a population of birds after vaccination compared to an unvaccinated group.
A vaccine comprising the polypeptide of the invention may reduce the number of oocysts shedded by the infected animals. Normally, the shedded oocysts will infect other animals in the flock. A decrease in the number of oocysts shedded will then also give a decrease in the number of animals which is subsequently infected and also a decrease in the number of oocysts shedded will give rise to a lesser infectious load.
Furthermore, even without effect on the parasite itself, a vaccine may decrease the incidence of disease. This is especially so when the symptoms of the disease are caused by products released by the parasite. Vaccines directed against such products alleviate the symptoms without attacking the parasite.
In any event it is preferred that a vaccine of the present invention is capable of reducing the number of cecal lesions in a bird when challenged with a subsequent Eimeria infection.
For live viral vector vaccines the dose rate per chicken may range from 103 to 108 pfu (but even  less than 1000 pfu might be sufficient e.g. for HVT). A typical subunit vaccine according to the invention comprises 0.1 to 100 xcexcg of the polypeptide (or variant or fragment thereof) according to the invention. Preferably at least 5 xcexcg will be present. Such vaccines can be administered intradermally, subcutaneously, intramuscularly, intraperitoneally, intravenously, orally or intranasally.
The vaccine according to the invention can also be effectively mixed with other antigenic components of the same and/or other Eimeria species, and/or with additional immunogens derived from a poultry pathogenic virus or micro-organism and/or nucleic acid sequences encoding these immunogens.
Such a combination vaccine can decrease the parasitic load in a flock of birds and can increase the level of protection against coccidiosis, and in addition protect against other poultry pathogens.
Those other immunogens may e.g. be selected from the group of poultry pathogenic viruses or micro-organisms consisting of Marek""s Disease virus (MDV), Newcastle Disease virus (NDV), Infectious Bronchitis virus (IBV), Chicken Anaemia Agent (CAA), Reo virus, Avian Retro virus, Fowl Adeno virus, Turkey Rhinotracheitis virus, Salmonella spp. or E. Coli. Thus a multivalent vaccine may be provided.
Still another embodiment of the invention relates to methods for the preparation of a vaccine.
Such methods comprise the admixing of a polypeptide according to the invention or an immunogenic fragment thereof and a pharmaceutically acceptable carrier.
An alternative and efficient way of vaccination is direct vaccination with DNA encoding the relevant antigen. Direct vaccination with DNA encoding polypeptides has been successful for many different polypeptides. (As reviewed in e.g. Donnelly et al., The Immunologist 2: 20-26 (1993)). In the field of anti-parasite vaccines, protection against e.g. Plasmodium yoelii has been obtained with DNA-vaccination with the Plasmodium yoelii circumsporozoite gene (Vaccine 12: 1529-1533 (1994)). Protection against Leishmania major has been obtained with DNA-vaccination with the Leishmania major surface glycoprotein gp63 gene (Vaccine 12: 1534-1536 (1994)).
Antibodies or derivatives thereof (e.g. fragments such as Fab, F(abxe2x80x2)2 or Fv fragments), which are directed against a polypeptide according to the invention have potential uses in passive immunotherapy, diagnostic immunoassays and in the generation of anti-idiotypic antibodies. Preferably these are specific for the Eimeria polypeptides of the present invention or variants/fragments thereof. Serum comprising antibodies or derivatives thereof may also be provided.
The Eimeria polypeptides (or variants or fragments thereof) as characterised above can be used to produce antibodies, which may be polyclonal, monospecific or monoclonal (or derivatives thereof). If polyclonal antibodies are desired, techniques for producing and processing polyclonal sera are known in the art (e.g. Mayer and Walter, eds. Immunochemical Methods in Cell and Molecular Biology, Academic Press, London, 1987).
Monoclonal antibodies, reactive against the Eimeria polypeptides (or variants or fragments thereof) according to the present invention, can be prepared by immunising inbred mice by techniques known in the art (Kohler and Milstein, Nature, 256, 495-497, 1975).
Anti-idiotypic antibodies are immunoglobulins which carry an xe2x80x9cinternal imagexe2x80x9d of the antigen of the pathogen against which protection is desired and can be used as an immunogen in a vaccine (Dreesman et al., J. Infect. Disease, 151, 761, 1985). Techniques for raising anti-idiotypic antibodies are known in the art (MacNamara et al., Science 226, 1325, 1984).
Antibodies against any of the polypeptides of the present invention and made e.g. in one of the manners described above, can be used i.a. for vaccination purposes, especially in immunocompromised animals.
Therefore, still another embodiment of the present invention relates to antibodies against any of the polypeptides according to the invention.
Also the invention relates to methods for the preparation of such antibodies. Those methods comprise the administration of a polypeptide according to the invention to a suitable animal, i.e. an animal capable of making antibodies against polypeptides.
It may be desirable to detect Eimeria as the cause of disease in poultry: especially early detection of Eimeria infection in a flock offers the opportunity to take adequate measures for the prevention of spreading of the infection. Detection of Eimeria infection can be done by detecting the Eimeria parasite in the host or by detecting host antibodies against Eimeria.
Detection of Eimeria parasites can be done e.g. as follows: DNA prepared from the contents of the digestive tract of a sick animal can be probed with DNA fragments according to the invention and submitted to standard Polymerase Chain Reaction (PCR). If Eimeria DNA is present, even in extremely low amounts, this will result in a PCR-product, visible on standard agarose gels after several rounds of PCR. PCR-techniques are e.g. described in Maniatis/Sambrook (Sambrook, J. Molecular cloning: a laboratory manual. ISBN 0-87969-309-6)
Therefore, the invention in still another embodiment relates to methods for the detection of Eimeria, which methods comprise incubating a DNA preparation isolated from poultry with a DNA fragment according to the invention.
Alternatively, antibodies against Eimeria can be detected. Detection of antibodies can e.g. be done using an ELISA assay, in which a polypeptide according to the invention is coated to the wall of an ELISA plate. The first step of such an ELISA may e.g. comprise adding serum of the animal to be tested to the ELISA plate. Antibodies against Eimeria, if present at all will bind to the polypeptide coated to the wall. The absence or presence of these antibodies can in a next step i.a. be detected by incubation with a labelled anti-poultry antibody. If antibodies against Eimeria were present in the serum to be tested, the labelled anti-poultry antibody will bind to them and the label will reveal their presence. These standard techniques are extensively described in xe2x80x9cAntibodies: a laboratory manualxe2x80x9d by Harlow, E. and Lane D. ISBN 0-87969-314-2
Therefore, the invention in still another embodiment relates to methods for the detection of Eimeria, which methods comprise the detection of host anti-Eimeria antibodies against any of the polypeptides according to the present invention.